1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
Like magnetic heads for longitudinal magnetic recording, magnetic heads for perpendicular magnetic recording typically used have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head comprises a magnetic pole layer that produces a magnetic field in the direction orthogonal to the surface of the recording medium.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in write characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the write characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, suffers degradation. It is therefore required to achieve better write characteristics as the track width is reduced.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has a medium facing surface that faces toward a recording medium. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew occurs, problems arise, such as an occurrence of a phenomenon in which data stored on an adjacent track is erased when data is written on a specific track (that is hereinafter called adjacent track erase), or unwanted writing between adjacent two tracks. To achieve higher recording density, it is required to suppress adjacent track erase. Unwanted writing between adjacent two tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
A technique is known for preventing the above-described problems resulting from the skew, as disclosed in U.S. Pat. No. 6,504,675 B1, for example. According to this technique, an end face of the pole layer located in the medium facing surface is made to have a shape in which one of the sides of the end face located backward along the direction of travel of the recording medium (that is, the side-located closer to the air inflow end of the slider) is shorter than the opposite side.
As a magnetic head for perpendicular magnetic recording, a magnetic head comprising the pole layer and a shield is known, as disclosed in U.S. Pat. No. 4,656,546, for example. In the medium facing surface of this magnetic head, an end face of the shield is located forward of the end face of the pole layer along the direction of travel of the recording medium with a specific small space therebetween. Such a magnetic head will be hereinafter called a shield-type head. In the shield-type head the shield prevents a magnetic flux from reaching the recording medium, the flux being generated from the end face of the pole layer and extending in directions except the direction orthogonal to the surface of the recording medium. In addition, the shield has a function of returning a magnetic flux that has been generated from the end face of the pole layer and has magnetized the recording medium. The shield-type head achieves a further improvement in linear recording density.
U.S. Pat. No. 4,672,493 discloses a magnetic head having such a structure that magnetic layers are respectively provided forward and backward of a middle magnetic layer to be a pole layer along the direction of travel of a recording medium and that coils are respectively provided between the middle magnetic layer and the magnetic layer located forward and between the middle magnetic layer and the magnetic layer located backward. According to this magnetic head, it is possible to increase components in the direction orthogonal to the surface of the recording medium among components of the magnetic field generated from an end of the middle magnetic layer closer to the medium facing surface.
U.S. Pat. No. 6,954,340 B2 discloses a magnetic head having such a structure that return poles are respectively provided forward and backward of a main pole to be a pole layer along the direction of travel of a recording medium and that coils are respectively provided between the main pole and the return pole located forward and between the main pole and the return pole located backward. This magnetic head has two side shields that connect the two return poles to each other and that are disposed on both sides of the main pole opposed to each other in the direction of track width.
Reference is now made to FIG. 37 to describe a basic configuration of the shield-type head. FIG. 37 is a cross-sectional view of the main part of an example of the shield-type head. This shield-type head comprises: a medium facing surface 100 that faces toward a recording medium; a coil 101 for generating a magnetic field corresponding to data to be written on the medium; a pole layer 102 having an end located in the medium facing surface 100, allowing a magnetic flux corresponding to the field generated by the coil 101 to pass, and generating a write magnetic field for writing the data on the medium by means of the perpendicular magnetic recording system; a shield layer 103 having an end located in the medium facing surface 100 and having a portion located away from the medium facing surface 100 and coupled to the pole layer 102; a gap layer 104 provided between the pole layer 102 and the shield layer 103; and an insulating layer 105 covering the coil 101. An insulating layer 106 is disposed around the pole layer 102. The shield layer 103 is covered with a protection layer 107.
In the medium facing surface 100, the end of the shield layer 103 is located forward of the end of the pole layer 102 along the direction T of travel of the recording medium with a specific space created by the thickness of the gap layer 104. At least part of the coil 101 is disposed between the pole layer 102 and the shield layer 103 and insulated from the pole layer 102 and the shield layer 103.
The coil 101 is made of a conductive material such as copper. The pole layer 102 and the shield layer 103 are made of a magnetic material. The gap layer 104 is made of an insulating material such as alumina (Al2O3). The insulating layer 105 is made of photoresist, for example.
In the head of FIG. 37 the gap layer 104 is disposed on the pole layer 102 and the coil 101 is disposed on the gap layer 104. The coil 101 is covered with the insulating layer 105. One of the ends of the insulating layer 105 closer to the medium facing surface 100 is located at a distance from the medium facing surface 100. In the region from the medium facing surface 100 to the end of the insulating layer 105 closer to the medium facing surface 100, the shield layer 103 faces toward the pole layer 102 with the gap layer 104 disposed in between. Throat height TH is the length (height) of the portions of the pole layer 102 and the shield layer 103 facing toward each other with the gap layer 104 disposed in between, the length being taken from the end closer to the medium facing surface 100 to the other end. The throat height TH influences the intensity and distribution of the field generated from the pole layer 102 in the medium facing surface 100.
The location of the end of a bit pattern to be written on a recording medium by the head of FIG. 37 is determined by the location of an end of the end face of the pole layer 102 located in the medium facing surface 100, the end being located forward along the direction T of travel of the recording medium. At a location forward of the end face of the pole layer 102 along the direction T of travel of the recording medium, the shield layer 103 takes in a magnetic flux generated from the end face of the pole layer 102 and extending in directions except the direction orthogonal to the surface of the recording medium. The shield layer 103 thereby prevents this flux from reaching the recording medium. As a result, it is possible to prevent a direction of magnetization of the bit pattern already written on the medium from being changed due to the effect of the above-mentioned flux.
In the shield-type head as shown in FIG. 37, for example, it is preferred to reduce the throat height TH to improve the overwrite property. It is required that the throat height TH be 0.1 to 0.3 micrometer (μm), for example. When such a small throat height TH is required, the following problems arise in the head of FIG. 37.
That is, when the head of FIG. 37 is in operation, the insulating layer 105 may expand due to the heat generated by the coil 101, and an end portion of the shield layer 103 closer to the medium facing surface 100 may thereby protrude. Particularly when the throat height TH is small, a portion of the shield layer 103 located between the insulating layer 105 and the medium facing surface 100 is thin, so that the end portion of the shield layer 103 closer to the medium facing surface 100 is more likely to protrude. The protrusion of the end portion of the shield layer 103 during operation of the head makes a collision of the slider with the recording medium occur more frequently.
According to the magnetic head comprising two coils disposed to sandwich the pole layer, as disclosed in U.S. Pat. No. 4,672,493 and U.S. Pat. No. 6,954,340 B2, it is possible to make the heat value of each of the two coils smaller than that of a coil of a magnetic head in which the coil is the only one coil provided.
However, the magnetic heads disclosed in U.S. Pat. No. 4,672,493 and U.S. Pat. No. 6,954,340 B2 have problems as will now be described. First, in the magnetic head disclosed in U.S. Pat. No. 4,672,493, at a location away from the medium facing surface, the magnetic layer located forward is connected to the top surface of the middle magnetic layer, and the magnetic layer located backward is connected to the bottom surface of the middle magnetic layer. In addition, the interface between the middle magnetic layer and the magnetic layer located forward and the interface between the middle magnetic layer and the magnetic layer located backward are opposed to each other. Therefore, in this magnetic head, in a region between these two interfaces, the flow of a magnetic flux that has come into the middle magnetic layer from the magnetic layer located forward and the flow of a magnetic flux that has come into the middle magnetic layer from the magnetic layer located backward are nearly opposite in direction. As a result, in the middle magnetic layer of this magnetic head, there occurs repulsion between the magnetic flux that has come into the middle magnetic layer from the magnetic layer located forward and the magnetic flux that has come into the middle magnetic layer from the magnetic layer located backward, and the flux density of the middle magnetic layer may be thereby reduced, which may result in degradation of overwrite property.
In the magnetic head disclosed in U.S. Pat. No. 6,954,340 B2, at a location away from the medium facing surface, the return pole located forward is connected to the top surface of the main pole with a first magnetic stud disposed in between, and the return pole located backward is connected to the bottom surface of the main pole with a second magnetic stud disposed in between. In addition, the interface between the main pole and the first magnetic stud and the interface between the main pole and the second magnetic stud are opposed to each other. Therefore, in this magnetic head, in a region between these two interfaces, the flow of a magnetic flux that has come into the main pole from the return pole located forward via the first magnetic stud and the flow of a magnetic flux that has come into the main pole from the return pole located backward via the second magnetic stud are nearly opposite in direction. As a result, in the main pole of this magnetic head, there occurs repulsion between the magnetic flux that has come into the main pole from the return pole located forward via the first magnetic stud and the magnetic flux that has come into the main pole from the return pole located backward via the second magnetic stud, and the flux density of the main pole may be thereby reduced, which may result in degradation of overwrite property.